In Emacs version 25.1.1 (and probably other versions), tab completion not work for function names unless they are enclosed in parentheses or quoted. For instance, after running emacs -Q, setting tab-always-indent to 'complete and attempting to complete "seq-" after (require 'seq), no completions are offered. However, "(seq-" completes as one would expect.

Is there a way to complete function names outside of quotes?

Edit: this issue also occurs with normal functions and not just generic ones as pointed out in the comments.

Edit: If helm is used for completion, one approach is to use the following code:

Assuming you're in emacs-lisp-mode you should take a look at elisp-completion-at-point that explicitly checks for "function position" with (eq (char-before beg) ?\(). A (seq- TAB (or a 'seq-) will therefore complete all seq functions as expected.
– mutbuergerJan 5 '17 at 9:38

In 26.0.50.2, I start with emacs -Q, then do M-x emacs-lisp-mode, and (require 'seq) (setq tab-always-indent 'complete) and then a TAB does show completions. Can you try in emacs -Q? Do you get completions for other libraries? What do you mean by "generic"?
– unhammerJan 5 '17 at 11:50